Thursday, February 27, 2014

A Better Blood Test For Down's Syndrome?

Presently, moms-to-be are offered prenatal screening for a third chromosome number 21 by either blood tests, ultrasound, or a combination of the two. Recently, a newer blood test was cleared for use in women at higher risk - eg. older women or those with abnormal ultrasound findings. The use of this test, involving examining the cell-free dna in mom's circulation, for women at lower risk is still considered investigational. As such, the test, called Noninvasive Prenatal Testing or NIPT, in low risk women is not recommended by specialty societies and not covered by insurance plans.

Yesterday's publication by Drs. Diana Bianchi, Rajeevi Madankumar and many other investigators in the New England Journal of Medicine brings this test one step closer to more widespread usage.

In conclusion. our head-to-head comparison showed that noninvasive prenatal cfDNA testing performed better than standard screening methods, with an improvement by a factor of 10 in the positive predictive value for trisomy 21 in our predominantly low-risk patient population. The major advantage of using cfDNA testing was the reduction in rates of false positive results. A consideration of cost-effective ways to incorporate cfDNA testing into general obstetrical practice26 is beyond the scope of this study. Our findings, however, suggest that cfDNA testing merits serious consideration as a primary screening method for fetal autosomal aneuploidy.

It is still far to early to recommend widespread introduction of this test. The study was not meant to be a head to head comparison of present screening practice vs NIPT. The test was less predictive in one major chromosome syndrome other than Down's. Nevertheless, NIPT's lower false positive rate would mean fewer anxious moments, fewer invasive procedures, and fewer losses of normal wanted babies.

Faster, please.

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